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How the brain switches between sleep and wakefulness is an open question, but in the worm Caenorhabditis elegans it seems the process occurs passively.

Manuel Zimmer and his colleagues at the Research Institute of Molecular Pathology in Vienna used a new calcium-imaging technology to simultaneously view the activity of most of the worm’s brain cells during a particular stage of larval development. During this stage the creatures are prone to falling asleep — providing oxygen levels remain as low as those in their normal soil environment.

When the scientists lowered oxygen levels, around three-quarters of the neurons became silent. Those not silenced included neurons responsible for monitoring alarming environmental signals such as high oxygen levels, and these caused the animals to awaken when the scientists raised oxygen levels.

This indicates that sleep is an emergent property of neuronal circuits, rather than an activity strictly enforced by specific brain areas, as others have suggested.

Autonomy-enhancing software has sped up exploration of Mars geochemistry.

The use of artificial intelligence (AI) in space exploration — instead of human commands sent all the way from Earth — saves precious mission time and has boosted the speed at which the Mars Curiosity rover gathers data.

The AEGIS software is designed to allow the robot to autonomously select appropriate rock and soil targets for analysis, and has been in routine use since NASA scientists installed it in May 2016. Raymond Francis at the Jet Propulsion Laboratory in Pasadena, California, and his colleagues now report that the software’s performance in selecting desired target material for the rover’s Chemistry and Camera (ChemCam) instrument exceeds 93% in unknown territory. Having Curiosity pick targets at random would yield a success rate of only about 24%, they estimate.

Organic particle behaviour may predict less carbon stored in the sea bed.

The ocean’s biological carbon pump may be shuttling less carbon from the surface to the depths than is assumed in most climate models.

Chelsey Baker of the National Oceanography Centre in Southampton, UK, and her colleagues analysed the amount of particulate organic carbon — microscopic detritus from marine life — in samples taken from 144 locations during eight Atlantic Ocean cruises from 2009 to 2013. The results suggest that the bulk of the carbon in the deep ocean is in the form of small particles, partly because larger ones become fragmented in midwater. But smaller particles sink more slowly than large ones and so are more likely to be chemically broken down before they reach the ocean floor, where they can be locked into sediment.

The researchers suggest that biogeochemical models, which assume a larger proportion of big, fast-sinking particles at great depths, might overestimate long-term carbon storage in the ocean.

The widespread use of air guns in underwater seismic surveys could be dramatically reducing populations of the microscopic animals at the base of the marine food chain.

Plankton are vital for the health of ocean ecosystems, but their sensitivity to human-made noise is not well understood. Robert McCauley at Curtin University in Perth, Australia, and his team decided to investigate the effects of air-gun signals, similar to those used for the detection of oil reserves, in a bay in Tasmania. They towed nets through the water before and after firing an air gun, and found that the abundance of collected zooplankton fell by more than 60% within an hour of the noise impulse, and that the number of dead animals more than doubled.

Sonar measurements suggest that zooplankton abundance dropped more than a kilometre away from the source of the gun shot.

A deadly fungus that causes skin lesions in snakes has been detected in wild European species for the first time.

Snake fungal disease, caused by Ophidiomyces ophiodiicola, infects at least 30 wild species in North America and can be fatal, but until now had not been reported in wild snakes on other continents.

Becki Lawson at the Institute of Zoology in London and her colleagues screened more than 300 moulted snake skins and around 30 carcasses, from 3 species in the United Kingdom and 1 in the Czech Republic. They found skin lesions on nearly one-quarter of carcasses and moulted skins. DNA analysis confirmed O. ophiodiicola infection in 31% of these samples, including grass snakes (Natrix natrix) and a dice snake (Natrix tessellata).

The European strains of the fungal pathogen were distinct from the North American ones. They were slower-growing and may have existed at low levels in Europe for years, the authors say.

An imaging technique used in cancer research and for diagnosing eye and heart disease has received a boost in resolution.

Optical coherence tomography allows scientists to map fine structure in living tissue, but it is limited by an image artefact called speckle. This is caused by interference that occurs when the laser beam strikes rough tissue surfaces.

Current speckle-reduction methods degrade image resolution. A team led by Adam de la Zerda at Stanford University in California improved on these by modulating the phase of the beam to vary the speckle pattern, and by capturing up to 100 different images that were stacked and averaged to almost eliminate speckle noise.

The improved technique can resolve structures as small as sweat ducts on a human fingertip and the inner structure of a live mouse’s cornea.

Blood test offers a way to identify those most likely to benefit from treatment for prostate cancer.

DNA floating in the blood provides a window into how people with prostate cancer will fare on drugs known as PARP inhibitors.

PARP inhibitors are used to treat tumours with mutations that disrupt particular DNA-repair pathways. Johann de Bono of the Institute of Cancer Research in London and his colleagues analysed blood samples from 46 people with prostate cancer in a clinical trial of the PARP inhibitor olaparib.

The team found that the amount of tumour DNA in the blood tended to fall more markedly in participants whose tumours shrank following therapy. In some patients who initially responded to treatment but then relapsed, the researchers detected additional mutations that corrected the original DNA-repair defect, allowing tumours to escape the effects of olaparib.

More than two billion people face at least 20 days of potentially lethal temperatures each year.

Heatwaves have killed thousands of people in 164 cities around the world since 1980 — and the risk of such events looks set to increase.

To identify climatic conditions associated with unusually high human mortality rates, Camilo Mora at the University of Hawaii at Manoa, Honolulu, and his colleagues analysed more than 900 papers published between 1980 and 2014. From this, they determined a threshold beyond which air temperatures, humidity and other factors can be lethal, and found that about 30% of the global population is currently exposed to potentially deadly heat for at least 20 days per year.

Climate projections suggest that by 2100, that percentage will be at least 48%, even if greenhouse-gas emissions are aggressively reduced. Heat-related health risks and mortality are likely to rise disproportionately in cities and humid regions in the tropics, the authors say.

Wildfires pollute the air more than previously thought — especially when it comes to tiny particles that can lodge in the lungs and cause health problems.

Greg Huey at the Georgia Institute of Technology in Atlanta and his colleagues analysed data gathered by research aeroplanes from the smoke plumes of three major wildfires in the western United States in 2013. The burns emitted more than three times the amount of fine particulate matter, or soot, accounted for in the US National Emissions Inventory.

Earlier estimates of the amount of particulate matter produced by such fires came from controlled burns, but it seems wildfires release much more pollution into the air. The team also measured a range of chemicals coming from the wildfires, including some nitrate compounds spotted for the first time in plumes from burning biomass. Setting controlled burns that improve forest health and reduce the risk of devastating wildfires may be one way to prevent future air-quality problems, the authors say.